Aleksandrov S L, Antonov V K
Mol Biol (Mosk). 1987 Jan-Feb;21(1):147-58.
The model system for the proton transfer on the amide atom of the substrate leaving group based on the existence of "charge relay system" in the serine type proteases was analysed by the CNDO/2 method. The unfitness of this model to explain the action mechanism of serine proteases was shown. The model system for proton transfer with the water molecule as the intermediate acceptor of the Ser-195 proton was suggested and analysed by the same method. The acylation activation barrier of this system was shown to localize on the stage of synchronous transfer of the Ser-195 alcoholic proton and the water molecule proton hydrogen bound to the His-57 N epsilon 2-atom on the water molecule oxygen atom and the N epsilon 2-atom, respectively. The protonation of substrate in the case of the model system with the water molecule as the intermediate acceptor of proton was demonstrated to begin before the completion of the tetrahedral intermediate substance and the protonated from of the tetrahedral intermediate was shown to form only. A hypothesis considering the role of this water molecule as the nucleophilic reagent on the deacylation stage is presented.
基于丝氨酸型蛋白酶中“电荷中继系统”的存在，用CNDO/2方法分析了底物离去基团酰胺原子上质子转移的模型系统。结果表明该模型不适用于解释丝氨酸蛋白酶的作用机制。提出了以水分子作为Ser-195质子的中间受体的质子转移模型系统，并用相同方法进行了分析。结果表明，该系统的酰化活化能垒位于Ser-195醇质子与水分子氧原子上与His-57 Nε2原子氢键结合的水分子质子同步转移阶段。在以水分子作为质子中间受体的模型系统中，底物的质子化在四面体中间产物形成之前就开始了，并且仅显示出四面体中间产物的质子化形式。提出了一个关于该水分子在脱酰化阶段作为亲核试剂作用的假说。
